Heat balance in FCC process

ABSTRACT

In a fluid catalytic cracking (FCC) process and apparatus, the heat balance between the reactor and the regenerator of the FCC operation is partially uncoupled by transferring at least a portion of thermal energy from the reactor vessel riser to the regenerator vessel. The transfer of thermal energy results in a higher regenerating temperature. The thermal energy is recirculated to the bottom section of the reaction riser through a regenerated catalyst having higher temperature. Consequently, the outlet of the reaction vessel is maintained at a substantially constant temperature (e.g., 100° F.) and the rate of conversion of the oil feed and the octane number of gasoline produced in the process are increased.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to catalytic cracking of petroleum fractions.More particularly, this invention relates to an improved process ofconverting easily coked petroleum fractions into coke and valuablehydrocarbon products, such as gas, gasoline, light cycle gas oil andheavy cycle gas oil in a fluid catalytic cracking reactor.

2. Description of Prior Art

Conversion of various petroleum fractions to more valuable products incatalytic reactors is well known in the art. The petroleum industry hasfound the use of a fluid bed catalytic cracker reactor (hereinafter FCCreactor) particularly advantageous for that purpose. An FCC reactortypically comprises a thermally balanced assembly of apparatuscomprising a reactor vessel filled with a catalyst and a regeneratorvessel wherein spent catalyst is regenerated. The feed is converted inthe reactor vessel over the catalyst and coke simultaneously forms onthe catalyst, thereby deactivating the same. The deactivated (spent)catalyst is removed from the reactor vessel and conducted to theregenerator vessel, wherein coke is burned off the catalyst with air,thereby regenerating the catalyst. The regenerated catalyst is thenrecycled to the reactor vessel. The reactor-regenerator vessel assemblymust be maintained in steady state heat balance so that heat generatedby burning the coke provides sufficient thermal energy for catalyticcracking in the reactor vessel. The steady-state heat balance is usuallyachieved and maintained in the FCC reactors by controlling the rate offlow of the regenerated catalyst from the regenerator to the reactor.The rate of catalyst flow is normally controlled by means of a slidevalve in the regenerator-to-reactor conduit. The degree of opening ofthe slide valve is controlled by a conventional controlling meanscoupled to a temperature sensing means (e.g., a thermocouple, placed atthe outlet of the reactor) to maintain the desired temperature insidethe reactor.

The product stream of the catalytic cracker is usually fractionated intoa series of products, including: gas, normally conducted to gasconcentration plant; gasoline; light cycle gas oil; and heavy cycle gasoil. A portion of the heavy cycle gas oil is usually recycled into thereactor vessel and mixed with fresh feed. The bottom effluent of thefractionator is conventionally subjected to settling and the solidportion of the settled product is also recycled to the reactor vessel inadmixture with the heavy cycle gas oil and feed.

In a modern version of fluid catalytic cracking reactor, the regeneratedcatalyst is introduced into the base of a riser column or riser in thereactor vessel. The riser column serves a two-fold purpose: (1) totransfer the catalyst from the regenerator to the reactor, and (2) toinitiate cracking of the petroleum feed. The regenerated hot catalyst isadmixed in the riser inlet or upstream section of the riser (or in thebottom of the riser column if the riser column is positionedsubstantially vertically and the flow of the feed and the catalyst is inthe upward direction) with a stream of fresh feed and recycled petroleumfractions, and the mixture is forced upwardly through the column. Duringthe upward passage of the catalyst and of the petroleum fractions,through the riser the petroleum is cracked and reformed, and coke issimultaneously deposited on the catalyst. The fluid bed of the cokedcatalyst and of the cracked and reformed petroleum components is passedupwardly out of the riser and through a solid-gas separation system,e.g., a series of cyclones, at the top of the reactor. The crackedpetroleum fraction is conducted to product separation, while the cokedcatalyst passes to the regenerator vessel, and is regenerated therein,as discussed above.

Further details of FCC processes can be found in U.S. Pat. Nos.2,383,636 (Wurth); 2,689,210 (Leffer); 3,338,821 (Moyer et al.);3,812,029 (Snyder, Jr.); 4,093,537 (Gross et al.); and 4,118,338 (Grosset al.); as well as in Venuto et al., Fluid Catalytic Cracking withZeolite Catalysts, Marcel Dekher, Inc. (1979). The entire contents ofall of the above patents and publications are incorporated herein byreference.

FCC reactions are endothermic in nature with the highest temperatures ofabout 1000° to 1050° F. observed at the inlet of the riser andcontinually falling along the reaction path. The lowest outlettemperature at the riser top and at the top of the reactor must usuallybe maintained below certain limits, e.g., below about 1040° F., becauseof limitations in heat transfer capacity of the downstream distillationcolumns. In addition, excessive temperature may cause maintenanceproblems, such as undue riser expansion and mechanical stress on theexpansion joints. Conversely, temperatures in the upstream anddownstream part or section of the riser, often reach levels much higherthan those at the outlet of the riser. The term "downstream part orsection of the riser" is defined herein as the riser sectionintermediate the riser inlet and the outlet of the riser, the latterbeing the section where the suspension of catalyst, products andunconverted feed leaves the riser. Excessive temperatures are controlledby decreasing catalyst circulation rate, which lowers the mix inlettemperature. However, decreased catalyst circulation rate may lead tomore complete combustion of the coke on the catalyst. Less coke left onthe regenerated catalyst increases catalyst activity. This activityincrease leads to more coke yield and higher regenerator temperatures,causing the rate of the catalyst circulation to decrease even further,or, as is commonly referred to in the art, to "wind-down." Thiscondition must be noted quickly and appropriate steps must be taken torestabilize the heat balanced operation, wherein the heat generated byregeneration of the catalyst in the regenerator does not exceed thetemperature limits of optimum operation in the riser. Removal of theheat from the downstream portion of the riser to a heat sink (cooler)outside of the system, thereby uncoupling the heat balance, isinefficient because valuable heat energy is removed from the process.

It is a primary object of this invention to increase the yield of andthe octane number of gasoline produced in the FCC plant within thetemperature constraint imposed on the reactor by downstream heat removallimitations.

It is an additional object of this invention to increase temperaturelevels in the regenerator portion of the FCC plant without upsettingoverall heat balance of the process.

It is another object of this invention to provide an improved method ofcatalyst regeneration in the FCC plant.

It is yet another object of this invention to provide an improved FCCreactor/regenerator assembly apparatus wherein at least a portion of thereactor riser is equipped with a heat exchanging means.

Additional objects and advantages of this invention will become apparentto those skilled in the art from the study of this specification and ofthe appended claims.

SUMMARY OF THE INVENTION

These and other objects have been attained according to this inventionby providing a heat exchanging means in the FCC riser, the heatexchanging means being coupled to the regenerator. The heat exchangingmeans decreases the temperature of the downstream section of the riserand increases the temperature of the regenerator. The increasedtemperature in the regenerator results in a more efficient regenerationprocess. The heat is recirculated from the regenerator to the upstreamportion of the riser through the hotter catalyst, thereby resulting in ahigher upstream riser cracking temperature without affecting thesubstantially constant outlet riser temperature. The net result ofconducting the process in this manner is increased conversion of thefeed to the gasoline fraction and coke, and higher octane number of thegasoline obtained in the process.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of a reactor vessel/regeneratorvessel assembly of an FCC plant with air heat exchanging means.

FIG. 2 is a schematic representation of a reactor vessel/regeneratorvessel assembly of an FCC plant with steam heat exchanging means.

DETAILED DESCRIPTION OF THE INVENTION

The section of the FCC riser where the heat exchanging means is providedmay begin at a distance in the riser immediately above the oil nozzleinlet and it may extend for the entire length of the riser. In apreferred embodiment, the heat exchanging means begins at a distance of15% of the total riser length to 70% of the total riser length and endsat a distance of between 20% and 90% of the total riser length. In themost preferred embodiment, the heat exchanging means begins at adistance of 20 to 50% of the total riser length and ends at a distanceof 25 to 90% of the total riser length. The total riser length isdefined herein as the length extending from the discharge of the feedoil nozzle and terminating at the point of exit of the mixture of thecatalyst and cracked feed from the riser. Thus, in a typical risermeasuring 120 feet in length, the heat exchanging means begins, in themost preferred embodiment, at a distance of 24 to 60 feet, and ends at adistance of 30 to 108 feet.

The heat exchanging means may be any conventionally known heatexchanging means used in the industry, such as a tube heat exchangersurrounding the section of the riser, or a shell and tube heat exchangerdesign.

The heat exchanging means may conveniently be operated by air in the FCCreactor wherein air is used for regenerating spent catalyst in theregenerating vessel. In that event, the air can be supplied to the heatexchanging means from the inlet of the regenerator vessel, as shown inone specific embodiment illustrated in FIG. 1 and discussed in detailbelow. However, it will be obvious to those skilled in the art that anyother conventional heat exchanging material or medium may be used in theheat exchanging means, e.g., steam, as shown in the embodiment of FIG.2, discussed below. If the heat exchanging means, e.g., a heatexchanger, is operated by air supplied from the inlet of theregenerating vessel, it must have a surface area of at least 1200 squarefeet (ft²) to effect a temperature increase in the downstream section ofthe riser of about 5° F. Conversely, if steam is used as the heatexchanging medium, the surface area of the heat exchanging means must beat least 200 ft² to effect a similar temperature increase in thedownstream section of the riser. It will be obvious to those skilled inthe art that if higher or lower temperature increase in the regeneratoris desired, the surface area of the heat exchanging means will have tobe altered in a conventional manner. It will also be obvious to thoseskilled in the art that air may be used in the heat exchanging means atthe same temperature and pressure conditions at which it is supplied tothe regenerating vessel to regenerate the catalyst.

The heat removed from the riser is conducted directly to theregenerating vessel, if air is used as the heat exchange medium.Conversely, if heat exchange medium other than the catalyst regeneratingmedium is used, the heat exchange medium should not directly contact thecatalyst in the regenerator. Therefore, the heat exchange medium (fluid)is circulated in a closed loop which preheats the regenerating mediumupstream of the regenerator. In both cases, the net result of the heatexchange is a temperature increase of the catalyst in the regeneratingvessel which, in turn, increases the rate of the regeneration reaction.The increased temperature in the regenerating vessel results in morecomplete combustion of the coke which, in turn, provides a morecompletely regenerated catalyst having higher temperature. Thisregenerated high temperature catalyst is subsequently conducted to theupstream section of the riser in a conventional manner, wherein thehigher temperature of the catalyst facilitates more complete conversionof the oil feed, promotes higher gasoline and coke yield, and increasesoctane number of the gasoline produced in the process. A mixture of theoil feed and the hot regenerated catalyst now passes through theupstream section of the riser, wherein rapid conversion and cracking ofthe oil feed takes place, and then downstream in the riser whereinconversion continues to take place. In the heat exchange section of theriser, the heat exchanging means removes at least some of the heat fromthat section and transfers it to the regenerator vessel, as discussedabove. Accordingly, the temperature in the riser, downstream of the heatexchange means, is not allowed to exceed certain limits, which can beset on a case-by-case basis for a particular process and feed.Consequently, the temperature in the remaining downstream portion of theriser may now be controlled so that the temperature at the outlet of thereactor vessel (or top of the reactor in a vertical reactor havingreactants flowing upwardly) does not exceed the temperature which can betolerated downstream in the process, e.g., in the distillation columnsdownstream of the FCC reactor, which usually cannot toleratetemperatures higher than 1040° F.

The temperature in the outlet section of the reactor is conventionallymeasured by a temperature sensing means, such as a thermocouple 7 shownin FIG. 1. The control loop of the thermocouple 7 usually controls theslide valve 8 in the conduit 6 leading from the regenerator to theupstream section of the riser. Accordingly, if some of the heat isremoved from the riser before the heat-carrying mixture of catalyst andoil approaches the vicinity of the thermocouple 7, the thermocouple willsense lower temperature and therefore would not alter the operation ofthe valve 8.

The heat exchanging means in the riser is controlled by a separatecontrol loop, comprising a temperature sensing means, e.g., athermocouple, placed in the lower section of the regenerator vessel, anda controller coupled thereto, which, in turn, is coupled to and controlsa valve in a conduit delivering heat exchanging medium (e.g., air orsteam) to the heat exchanging means in the downstream section of theriser. Thus, if the temperature sensed by the temperature sensing meansin the lower section of the regenerator vessel is at the set point ofthe controller, the operation of the valve in the conduit for heatexchanging medium will not be altered. However, once the temperaturesensed by the heat exchanging means in the lower section of theregenerating vessel exceeds the set point, the controller activates thevalve in the conduit through which the heat exchanging means isconducted, thereby decreasing the flow thereof to the heat exchangingmeans in the upper section of the vessel. Accordingly, less heat istransferred from the riser to the regenerator and the temperature of thecatalyst in the regenerator decreases to about that of the set point ofthe controller. Conversely, if the temperature sensed by the heatsensing means in the lower section of the regenerator falls below theset point, the controller would again activate the valve to increase theflow of the heat exchanging medium to the heat exchanging means therebyincreasing the temperature in the regenerating vessel.

The apparatus used in the control loop for the heat exchanging means isthat conventionally used in the art for measuring and controllingtemperature of any process loop or parameter and its operation will bereadily apparent to those skilled in the art.

The control set point for the control device can be set at any desiredlevel depending on the type of oil feed used in the process, the type ofcatalyst, and the final product mix desired. However, the set pointshould be established at such a value that the temperature increase inthe upstream section of the riser resulting from the increasedtemperature of the catalyst is at least 2° F., preferably 5° F. to 50°F., and most preferably 10° F. to 30° F. Preliminary calculationsindicate that a 5° F. to 10° F. temperature increase in the upstreamsection of the riser would result in an increase of conversion by0.5-1.0% and an increase in the octane number of gasoline obtained inthe process by about 0.2-0.511.

The process of this invention can be used in conjunction with anycatalyst conventionally used in the FCC processes, e.g., zeolites,silica alumina, and zeolites with carbon oxide burning promoters.However, the process is particularly applicable to the FCC processeswherein carbon monoxide burning promoter is used. Such carbon monoxideburning promoters or carbon monoxide burning catalysts include: platinummetals, e.g., platinum, palladium, rhodium, ruthenium, iridium andosmium, and rhenium.

When carbon monoxide burning catalysts or carbon monoxide promoters wereused in prior art FCC processes, there was observed an increasedtemperature in the regenerator because of additional conversion ofcarbon monoxide to carbon dioxide. As a result, the temperature of theregenerated catalyst introduced into the upstream section of the riserfrom the regenerator was also increased. Accordingly, the conventionallyused temperature control loop discussed above, which maintained thetemperature at the outlet portion of the FCC reactor at below thepre-set limit (e.g., 1000° F.), activated the slide valve in theregenerator-to-reactor conduit to decrease the rate of flow of the hotregenerated catalyst to the upstream section of the riser. This change,of course, decreased the rate of conversion of the oil feed in the riserand octane number of the gasoline product.

However, if the process is operated in accordance with the presentinvention, returning a portion of the additional heat generated by thecarbon monoxide (CO) burning catalyst to the regenerator, before itreaches the outlet of the riser and of the reactor, results in theoutlet reactor controller sensing a lower outlet temperature increase,and therefore in a smaller reduction of the catalyst circulation rate.In other words, the decrease in the circulation rate of the catalyst dueto increased temperature in the regeneration vessel is smaller than itwould otherwise be without the presence of the heat exchanging means inthe riser.

Similarly, any sudden decrease in the temperature of the regenerator cannow be easily and relatively quickly corrected by increasing the flow ofa heat exchanging medium to the heat exchange means in the downstreamsection of the riser. The increase in the rate of flow of the heatexchanging means, in response to a decreasing temperature in theregenerator, would transfer additional heat to the regenerator, therebycorrecting the temperature imbalance therein. It is well known in theart that any change in the operation of the regenerator of prior art FCCreactors which causes sudden temperature drop has a profound and lastingeffect on the operation of the entire FCC system. More particularly, thesudden drop in the temperature of the regenerator must be remedied inthe prior art systems by increasing the rate of catalyst flow from theregenerator to the upstream section of the riser. This, in turn, causesincreased coke yield. Higher catalyst circulation results in anincompletely regenerated catalyst and in lower regenerator temperatures.The net result of all of these changes is a sudden and severe upset ofheat balance between the FCC reactor and the regenerator. This conditionis commonly known in the art as "wind-up." The symptoms of wind-up mustbe noticed quickly and corrective action taken immediately, forotherwise there is a danger of permanently upsetting the operation ofthe FCC reactor.

The use of the heat exchanging means, in accordance with the presentinvention, provides an expeditious method of controlling the wind downor the wind-up conditions, both discussed above, by transferring aportion of the heat from the riser to the regenerator vessel, andsubsequently recycling the additional heat from the regenerator to thereactor through the hotter catalyst. In this manner, all of the heatgenerated internally in the process is conserved and used in the processwithout upsetting the delicate heat balance between the reactor and theregenerator vessels.

In a similar manner, the process of the present invention also affords aconvenient means of maintaining the steady state heat balance of the FCCreactor which may otherwise be upset by changed product mix and/oroperating conditions thereof.

The heat exchanging medium used in the heat exchanger is preferably thesame medium, i.e., the same fluid, which is used for regenerating thecatalyst in the regenerator vessel. The air regenerating medium isusually introduced through the bottom of the regenerator to provideefficient mixing of the regenerating medium with the coked catalyst.With the present invention, a portion of the air, e.g., about 10% of thestream, is diverted from the conduit introducing the regenerating mediuminto the regenerator vessel and it is passed through the heat exchangingmeans placed about the riser. After passing through the heat exchangingmeans, the air is conducted into the regenerating vessel through aseparate conduit, preferably terminating with a grid distributionpattern, separate and distinct from the primary inlet for theregenerating medium in the regenerating vessel, and is discharged intothe bed of catalyst in the regenerating vessel. The grid distributionpattern may be positioned above an inverted circular cup plate,preferably provided for distribution of the suspension, or at any otherconvenient location in the regenerator. It will be apparent to thoseskilled in the art that the exact location of the grid distributionpattern is not critical, as long as it efficiently transfers thermalenergy from the riser to the regenerator.

It will be obvious to those skilled in the art that any conventionalheat exchanging medium (fluid) may be used in the heat exchanging meansof this invention. If the heat exchanging medium is other than that usedfor regenerating the catalyst in the regenerator vessel, it may beintroduced from an outside source into the heat exchanging means, thenconducted to a regenerating medium preheater upstream of theregenerator, and recycled back into the heat exchanging means. Asuitable alternative heat exchanging fluid is steam, as discussed belowin connection with the embodiment of FIG. 2.

The heat exchanging means placed about the riser is preferably aconventional heat exchanger which allows the heat exchanging medium topass directly in contact with the outer shell of the downstream sectionof the riser, thereby enabling it to remove some of the thermal energy(heat) from the riser and transfer it to the heat exchanging medium. Forgreater contact surface area, the heat exchanging means may be comprisedof a number of convoluted tubes surrounding the riser for a desiredlength thereof. However, it will be obvious to those skilled in the artthat any conventionally known heat exchanging equipment can be placedabout the riser, as long as the desired degree of heat exchange betweenthe riser and the heat exchanging medium is accomplished.

As discussed above, the heat exchanging means is controlled and operatedby a control loop, an essential element of which is a temperaturesensing means placed in the regenerator vessel. The temperature sensingmeans is, e.g., a thermocouple, or any other conventionally usedtemperature sensing device.

The temperature sensing means is preferably placed downstream of the cupplate and of the grid distribution patterns introducing the catalystregeneration medium and the heat exchanging medium, respectively, intothe regenerating vessel. This preferred placement of the heat sensingmeans allows for thorough mixing of the catalyst before it comes intocontact with the temperature sensing means of the control loop, therebyallowing the temperature sensing means to sense and record thetemperature of the catalyst shortly after its introduction into theregenerator. However, it will be obvious to those skilled in the artthat the exact location of the temperature sensing means is notcritical, as long as it aids in maintaining the temperature at theoutlet of the reactor vessel at the desired level. The optimum locationof the heat sensing means can be easily calculated by those skilled inthe art on a case-by-case basis.

It will also be obvious to those skilled in the art that the FCC processand the apparatus of this invention are equipped with a number of othercontrol loops conventionally used in the FCC installations and theoperation of these conventional loops can be integrated with and/or canbe kept independent of the operation of the control loop for theexchanging means. Such conventionally used control loops are fullydisclosed in the patents and publications cited above.

Thus, for example, the embodiment of FIG. 1, discussed in detail below,includes a conventional control loop (disclosed, e.g., in U.S. Pat. No.4,093,537) controlling the rate of air flow into the regenerator. Suchcontrol loop includes a composition sensor 29 which indicates the carbonmonoxide and oxygen content of the flue gas, and generates a signalindicative of that composition. Valve 21 is commonly controlled byoperator intervention to control the flow of air and thus the CO andoxygen content of the flue gas. Alternatively, the signal generated bycomposition sensor 29 is transmitted to the composition controller 25.Controller 25, equipped with set points 27, places a signal on line 23,which signal is indicative of the deviation of the carbon monoxidecomposition of the flue gas from the set point 27 to adjust the controlvalve 21 in a direction to reduce the deviation of the measuredcomposition from the predetermined composition as defined by the setpoint 27. In general, the set point is adjusted to a CO content lessthan 2000 ppm and the flue gas, in general, will contain about 2% excessoxygen gas. A similar conventional air rate control loop is provided inthe embodiment of FIG. 2 with all of the parts of the loop numbered in amanner similar to that of FIG. 1 with a prefix of 100, e.g., thecontroller 125 in FIG. 2 corresponds to the controller 25 in FIG. 1,etc. It will be apparent to those skilled in the art that the air ratecontrol loop of the embodiment of FIG. 2 operates in a manner identicalto that of the embodiment of FIG. 1.

In reference to FIG. 1 exemplifying one of the embodiments of thepresent invention, a hydrocarbonaceous feed, e.g., a hydrocarbon oilfeed such as gas oil or higher boiling material, is introduced through aconduit 2 to the bottom or upstream section of riser reactor 4. Hotregenerated catalyst is also introduced to the bottom section of theriser by a standpipe 6 equipped with a flow control valve 8. The degreeof opening of the control valve 8 is controlled by a control loopcomprised of a temperature sensing means 7 at the top of the reactor anda controller 9, of a conventional type. A vapor liquid suspension isformed in the lower bottom section of the riser 4 at an elevatedtemperature at about 950° F., and usually at about 980° F. Thetemperature range of the suspension may vary from 980° F. to 1200° F.and is usually at least 1000° F., depending on the degree of thehydrocarbon conversion desired and on the composition of the feed. Thesuspension formed in the bottom section of the riser is passed upwardlythrough the riser under selected temperature and residence timeconditions. The residence time of the hydrocarbon charge stock in theriser is usually between 2 and 15 seconds, preferably 5 to 10 seconds,before the suspension passes through suitable separating means, such asa series of cyclones 11, rapidly effecting separation of catalystparticles from vapor hydrocarbon conversion products. Thus, in theapparatus shown in FIG. 1, the suspension is discharged from the riser 4into one or more cyclonic separators attached to the end of the riserand represented by a separator means 11. Catalyst particles separated inthe cyclone 11 pass counter-currently in contact with stripping gasintroduced by conduit 16 to a lower portion of the cyclone. The thuscontacted and separated catalyst is withdrawn by a dipleg 14 fordischarge into a bed of catalyst in the lower section of the reactor.

A tubular heat exchanger 10 surrounds the upper or downstream section ofthe riser. The heat exchanger is operated with air conducted theretothrough a conduit 43, branched off from a conduit 35 supplying the airto the regenerator vessel 36. The air (at the rate of, e.g., about32,000 lbs/hr) enters the heat exchanger through the conduit 43 at atemperature of about 300°-500° F. and pressure of 25-40 psig and exitsthe heat exchanger through a conduit 45 at the temperature of about 375°to 575° F. and pressure of 24 to 39 psig, and is thereafter conducted toa grid distribution 50 in the regenerating vessel, whereby it isdischarged into the bed of catalyst particles.

The mixture of the oil feed and catalyst proceeds upwardly through theriser 4 to the downstream end thereof. The end of the riser 4 withattached separation means 11 as shown in FIG. 1, is housed in a largervessel 17 designated herein as a receiving and catalyst collectingvessel. The lower portion of the vessel 17 has generally a smallerdiameter than the upper portion thereof, and it comprises a catalyststripping section 18 into which a suitable stripping gas, such as steam,is introduced, e.g., by a conduit 20. The stripping section is providedwith a plurality of baffle means 22 over which the downflowing catalystpasses counter-currently to upflowing stripping gas.

A separating means, e.g., a cyclone 24, is provided in the upper portionof the vessel 16 for recovering stripped hydrocarbon products andstripping gas from entrained catalyst particles. As is well known in theart, there may also be provided a second sequential stage (not shown inFIG. 1 for clarity) of catalyst separation for product vapors dischargedfrom the separator 11 by a conduit 26.

Stripped catalyst comprising carbonaceous deposits of the riserconversion section is withdrawn from the bottom of the stripping sectionat an elevated temperature, e.g., 1000° F., by a standpipe or conduit 30equipped with a flow control valve 32. The catalyst is then passed fromthe standpipe 30 into the bottom portion of regenerator riser 34. A liftgas is introduced into the bottom of riser 34 through a conduit 35. Thelift gas is selected from the group comprising air preheated air, andoxygen supplemented air at about 300° to 500° F. and about 40 psig. Theamount of lift gas introduced into the regenerator riser is sufficientfor forming a suspension of the catalyst in the lift gas, whichsuspension is forced to move upwardly through the riser 34 underincipient or partial regenerator conditions and into the bottom portionof an enlarged regenerator vessel 36. Regenerator vessel 36 comprises abottom closure member 38 shown in the drawing to be conical in shape.Other suitable shapes obvious to those skilled in the art, may also beemployed, such as rounded dish shapes.

The regenerator vessel 36 comprises in the lower section thereof asmaller diameter cylindrical vessel means 40 provided with a cylindricalbottom containing a cylindrical opening in the bottom thereof, whosecross-section is at least equal to the cross-section of the riser 34. Anouter cylindrical space 49 is formed by the chambers 36 and 40, and itserves to recirculate regenerated catalyst to the dense bed.

Vessel 40 is provided with a conical head member 46 terminating in arelatively short cylindrical section of sufficient vertical height andcapped at its upper end by means 47 to accommodate a plurality ofradiating arm means 48. The radiating arm means 48 are opened in thebottom side thereof because they are "U" shaped tunnels in cross-sectionand operate to discharge a concentrated stream of catalyst substantiallyseparated from combustion product gases generally downward into thespace 49. Vessel 40 is herein referred to as the combustor vesselbecause in this portion of the regenerator the combustion ofcarbonaceous material and the carbon monoxide formed during thecombustion is particularly promoted. The catalyst used in the processmay incorporate a carbon monoxide (CO)-burning promoter, e.g., platinum,palladium, iridium, osmium, rhodium, ruthenium and rhenium, described indetail in U.S. Pat. Nos. 4,072,600 and 4,093,535, the entire contents ofwhich are incorporated herein by reference. An inverted circular cupplate 52 may be used if desired to accomplish the distribution of thesuspension as mentioned above. In addition, a distributor grid 50,connected to the conduit 45 of the heat exchanger 12, is used in thelower cross-section of vessel 40 above the inverted circular or cupplate 52. A thermocouple 37 is placed in the bottom section of theregenerator vessel 36, just above the cup plate 52. The thermocouple 37measures the temperature of the catalyst in the regenerator bed, shortlyafter its introduction from the reactor to the regenerator and conveysthose measurements to a controller 39 which compares it with the setpoint thereof to arrive at a value of catalyst temperature deviation. Ifthe temperature sensed by the thermocouple 37 is below that of the setpoint in the controller 39, the controller 39 causes a valve 41 to openwider, thereby permitting a larger volume of the fluid introducedthrough a conduit 35 to flow into the heat exchanger. Conversely, if thetemperature sensed by the thermocouple 37 is above the set point in thecontroller 39, the opening of the valve 41 is decreased, therebydecreasing the rate of flow of the fluid through the conduit 43. Thesechanges result in the decrease of the value of the catalyst temperaturedeviation.

In the upper portion of vessel 36, a plurality of cyclonic separators 54and 56 is provided for separating combustion flue gases from entrainedcatalyst particles. The separated flue gases pass into plenum 58 forwithdrawal by a conduit 60. If significant combustion of carbon monoxidetakes place in the upper portion of vessel 36, above the annulus 44, aheat absorbing catalyst may be used in the process to improve the heatrecovery efficiency of the operation.

The regenerator vessel described above and shown in FIGS. 1 and 2, andthe method of operation thereof is designed to maintain during operationa substantial mass or bed of fluid regenerated catalyst particles in theouter annular zone 49. Fluidizing gas (i.e., regenerating medium), whichmay or may not contain oxygen to achieve complete combustion ofcarbonaceous deposits on the catalyst, is introduced into the lowerportion of the annular zone or segments of the annular zone by conduits62 and 64. The designation "segments" is intended to mean that onlyselected vertically oriented portions of the annular section beneath thedischarge of radiating arms 48 will contain regenerated catalyst. Thus,with this arrangement, the volume of regenerated catalyst retained inthe annular zone 49 can be considerably reduced over that retained byusing the total annulus. On the other hand, sufficient amount ofregenerated catalyst must be retained by the annular zone 49 to permitthe method of operation described herein and to maintain the heatbalance between the reactor vessel and the regenerator vessel. Thecatalyst regenerator operation illustrated herein is designed to provideregenerated catalyst at an elevated temperature above 450° F. andpreferably at 1300° to 1500° F., having residual coke on catalyst ofless than about 0.15 and preferably 0.01 to 0.05 weight percent.However, the process of the present invention can be successfully usedwith any regenerator operation coupled to an FCC reactor. Accordingly,the regenerator operation illustrated in the embodiments of FIGS. 1 and2 is used an an example of one suitable regenerator and is not to beconsidered a limitation of the present invention.

A portion of the regenerated catalyst at an elevated temperature of atleast 1200° F. is recycled by the catalyst pressure head developed inthe annular zone 49 for admixture with the spent catalyst passing fromthe riser 34 into the combustion section. The amount of recycle ofregenerated catalyst for admixture with spent catalyst is essentiallyself-controlling, once certain operating flow characteristics areestablished in the process, such as the catalyst flow rate to thehydrocarbon conversion zone (the reactor vessel), catalyst make-up rateto the operation, and the flow rate of the suspension passing upwardlythrough riser 34 and combustion section 40 of the regenerator. Thus, thesuspension of catalyst being subjected to regenerating conditions passesthrough gradations of catalyst particle concentration or density for agiven volume within the range of about 35 lbs/ft³ to about 10 lbs/ft³.Consequently, the combustion section 40 is not necessary to maintain adense fluid bed of catalyst with a significant interface between a moredispersed phase of catalyst above the combustion section. On the otherhand, the upflowing mass of catalyst may be maintained relativelyuniform in density until it encounters the conical head section andradiating discharge arms which accelerate the flow of the suspension andthus reduce the particle concentration per given volume.

Regenerated catalyst collected in the annulus or a section of theannulus is withdrawn by a standpipe 6 for passage to the riserhydrocarbon conversion zone 4. As mentioned above, the standpipe 6 isequipped with a control valve 8, operated by a control loop comprisingthe thermocouple 7 and the controller 9 connected to the valve 8. Thefunction of the thermocouple 7 and the controller 9 is to assure thatthe temperature of the mixture of hydrocarbon products and stripping gaswithdrawn through the conduit 28 does not exceed a limit allowable fordownstream processing of the hydrocarbon products, e.g., about 1000° F.Thus, if the temperature sensed by the thermocouple 7 exceeds thatlimit, the opening of the valve 8 is decreased thereby decreasing therate of flow of hot regenerated catalyst into the riser 4 and decreasingthe temperature of the hydrocarbon products exiting through the conduit28. However, this also results in the lower rate of conversion of theoil feed. Conversely, if the temperature sensed by the thermocouple islower than the 1000° F. set point of the controller 9, the opening ofthe valve 8 is increased, thereby allowing for higher rate of flow ofthe regenerated catalyst into the riser 4, resulting in higherconversion ratio and higher temperatures sensed by the thermocouple 7.However, as mentioned above, the use of the heat exchanger 12 in theriser enables one to cycle the regenerated catalyst into the riser at ahigher rate with the resulting increase in the rate of conversion of theoil and increased octane number of the gasoline produced, without thethermocouple 7 sensing unduly high temperature levels.

In an alternative embodiment illustrated in FIG. 2, the heat exchangingmedium is steam. Accordingly, the heat exchanging means is designed toprevent direct contact of steam with the catalyst being regenerated inthe regenerator vessel. A stream of steam, from an outside source atabout 420° F. and 320 psig, enters a heat exchanger 112 through conduits168 and 143. A portion of thermal energy is transferred from the riser104 to the steam in the heat exchanger 112. The steam exits the heatexchanger at about 470° F. and 530 psig and is then directed via aconduit 170 to a preheater 166 where the air used to regenerate thecatalyst is preheated with the steam before its introduction into theregenerator. The steam exits the preheater 166 through a conduit 172 andis then combined with the fresh steam in conduit 143. The air preheater166 is any conventional heat exchanging means, e.g., a shell and tubeheat exchanger. A thermocouple 137 senses the temperature of thecatalyst in the regenerator and conveys those measurements to acontroller 139 which compares it with the set point of the controller toarrive at a value of catalyst temperature deviation. If the temperaturemeasured by the thermocouple 137 is below the set point of thecontroller, the controller causes valve 141 to open wider, therebyforcing a larger volume of the steam to flow into the heat exchanger112. Conversely, if the temperature sensed by the thermocouple 137 isabove the set point of the controller 139, the opening of the valve 141is decreased and less steam flows into the heat exchanger 112. Thesechanges result in the decrease of the value of the catalyst temperaturedeviation. The air preheater 166 is also equipped with a conduit 131,optionally containing a valve, not shown in the drawing, for the removalof steam condensate. A valve 133 and a conduit 135 in the steam conduit143 provide a means for venting excess steam.

Aside from the use of the air preheater 166 and other auxiliaryequipment associated with the steam heat exchange means, the embodimentof FIG. 2 is operated in a manner identical to the embodiment of FIG. 1.All of the parts of the apparatus of FIG. 2 are numbered in a mannersimilar to that of FIG. 1 with a prefix of 100, e.g., oil feed inlet 2in FIG. 1 corresponds to feed inlet 102 in FIG. 2, etc. It is believedthat further operation of the embodiment of FIG. 2 will be apparent tothose skilled in the art from the detailed description of operation ofthe embodiment of FIG. 1, above.

As mentioned above, the catalyst regeneration system of this inventioncontemplates providing the catalyst with a carbon monoxide oxidationpromoter in an amount particularly promoting the combustion of formedcarbon monoxide to carbon dioxide within the region of high particleconcentration in the combustor. The oxidation promoter may be added inthe form of separate discrete catalyst particles or it may beincorporated in the cracking catalyst employed in the operation.Substantially any suitable cracking catalyst may be employed in thesystem of this invention, e.g., an amorphous catalyst, a crystallinealumina silicate catalyst or a mixture thereof. The process andapparatus of this invention is however particularly useful with higherand lower activity, preferably low coke-producing crystalline zeolitecracking catalyst comprising faujasite crystalline zeolites and otherzeolites known in the art in a regeneration procedure particularlypromoting the recovery of available heat generated by the burning ofcarbonaceous deposits produced in hydrocarbon conversion, such as thecatalysts disclosed in U.S. Pat. Nos. 3,748,251 and 3,886,060, theentire contents of which are incorporated herein by reference.

Similarly, the process of this invention can be used with any suitablefeed material which is amenable to processing in the FCC reactors. Suchsuitable feed materials include any conventional hydrocarbon feedstocks,e.g., naphthas, gas oil, vacuum gas oil, light and heavy distillates,residual oils and the like.

It will be apparent to those skilled in the art that the above exampleand general description of the process can be successfully repeated withingredients equivalent to those generically or specifically set forthabove and under variable process conditions.

From the foregoing specification one skilled in the art can readilyascertain the essential features of this invention and without departingfrom the spirit and scope thereof can adopt it to various diverseapplications.

What is claimed is:
 1. In a fluid catalytic cracking process comprisingadmixing a hydrocarbonaceous feed with a regenerated catalyst in theupstream section of a reactor riser, passing the hydrocarbonaceous feedand the catalyst admixed therewith through the downstream section of theriser, thereby effecting cracking of the hydrocarbonaceous feed at theprocess temperature under endothermic process conditions anddeactivating the catalyst by deposition of carbonaceous depositsthereon, separating the deactivated catalyst from the crackedhydrocarbonaceous feed, passing the deactivated catalyst to aregenerator vessel wherein the carbonaceous deposits are removed fromthe deactivated catalyst under exothermic process conditions by means ofa regenerating medium introduced into the regenerator vessel by aregenerating medium distribution means, thereby regenerating and heatingthe catalyst, and passing the regenerated hot catalyst to the upstreamsection of the reactor riser, the improvement wherein at least a portionof the thermal energy is transferred by heat exchanging means from theriser to the regenerator vessel.
 2. A process according to claim 1wherein the heat exchanging means comprises an air heat exchanger.
 3. Aprocess according to claim 1 wherein the heat exchanging means comprisesa steam heat exchanger.
 4. A process according to claim 2 wherein thecatalyst contains carbon monoxide burning promoter.
 5. A processaccording to claim 3 wherein the catalyst contains carbon monoxideburning promoter.
 6. A process according to claim 2 wherein the portionof the thermal energy transferred to the regenerator vessel isintroduced into the regenerator vessel above the regenerating mediumdistribution means.
 7. A process according to claim 3 wherein theportion of the thermal energy transferred to the regenerator vessel isintroduced into the regenerator vessel above the regenerating mediumdistribution means.
 8. A process according to claim 6 wherein the airheat exchanger is controlled by a temperature sensing means placed inthe regenerator vessel below the point of introduction of the portion ofthe thermal energy into the regenerator vessel.
 9. A process accordingto claim 7 wherein the steam heat exchanger is controlled by atemperature sensing means placed in the regenerator vessel below thepoint of introduction of the portion of the thermal energy into theregenerator vessel.
 10. A process according to claim 8 wherein the airheat exchanger has the surface area of at least 1200 square feet.
 11. Aprocess according to claim 9 wherein the steam heat exchanger has thesurface area of at least 200 square feet.
 12. A process according toclaim 10 wherein the carbonaceous deposits are removed from thedeactivated catalyst by air having a temperature of 300° to 500° F. 13.A process according to claim 11 wherein the carbonaceous deposits areremoved from the deactivated catalyst by air having a temperature of300° to 500° F.
 14. A process according to claim 12 wherein the air heatexchanger is placed about the riser at a distance beginning at 15% to70% of the total riser length and terminating at a distance of 20% to90% of the total riser length.
 15. A process according to claim 13,wherein the steam heat exchanger is placed about the riser at a distancebeginning at 15% to 70% of the total riser length and terminating at adistance of 20% to 90% of the total riser length.
 16. A processaccording to claim 15 wherein the steam after passing through the steamheat exchanger is conducted to the regenerating medium preheating meansto preheat the regenerating medium before the introduction thereof intothe regenerator vessel.
 17. A process according to claim 1 furthercomprising a method for controlling said process, whichcomprisescomparing the temperature of the catalyst in the regeneratorvessel with a predetermined temperature to obtain a catalyst temperaturedeviation; and controlling the rate of flow of a heat exchanging mediuminto the heat exchanging means in a direction to reduce the temperaturedeviation.
 18. In a fluid catalytic cracking process comprising admixinga hydrocarbonaceous feed with a regenerated catalyst in the upstreamsection of a reactor riser, passing the hydrocarbonaceous feed and thecatalyst admixed therewith through the downstream section of the riser,thereby effecting cracking of the hydrocarbonaceous feed at the processtemperature under endothermic process conditions and deactivating thecatalyst by deposition of carbonaceous deposits thereon, separating thedeactivated catalyst from the cracked hydrocarbonaceous feed, passingthe deactivated catalyst to a regenerator vessel wherein thecarbonaceous deposits are removed from the deactivated catalyst underexothermic process conditions by means of a regenerating mediumintroduced into the regenerator vessel by a regenerating mediumdistribution means, thereby regenerating and heating the catalyst, andpassing the regenerated hot catalyst to the upstream section of thereactor riser, the improvement wherein at least a portion of the thermalenergy is transferred by heat exchanging means from the riser to theregenerator vessel, thereby recovering an improved yield of gasolineproduct having higher octane over that obtainable at the same reactorvessel outlet temperature without the heat exchange means.
 19. In afluid catalytic cracking apparatus comprising a reactor vessel and aregenerator vessel, said reactor vessel comprising a riser divided intoan upstream section and a downstream section, said regenerator vesselcomprising a regenerating medium inlet conduit cooperating with aregenerating medium distribution means in the lower section thereof anda solid-gas separation means in the upper section thereof, a means forconveying a deactivated catalyst from said reactor vessel to saidregenerator vessel, a means for conveying a regenerated catalyst fromsaid regenerator vessel to said reactor vessel, a first means forsensing temperature at the outlet of said reactor vessel, said firstmeans for sensing temperature controlling said means for conveying theregenerated catalyst from said regenerator vessel to said reactorvessel, the improvement wherein said riser is equipped with heatexchanging means for transferring at least a portion of thermal energyfrom said riser to said regenerator vessel.
 20. An apparatus accordingto claim 19 wherein said heat exchanging means is an air heat exchanger.21. An apparatus according to claim 19 wherein said heat exchangingmeans is a steam heat exchanger.
 22. An apparatus according to claim 20wherein said air heat exchanger introduces said portion of thermalenergy into said regenerator vessel above said regenerating mediumdistribution means.
 23. An apparatus according to claim 21 wherein saidsteam heat exchanger introduces said portion of thermal energy into saidregenerator vessel above the regenerating medium distribution means. 24.An apparatus according to claim 22 further comprising a secondtemperature sensing means, placed in said regenerator vessel below thepoint of introduction of said portion of thermal energy by said air heatexchanger into said regenerator vessel, to control said air heatexchanger.
 25. An apparatus according to claim 23 further comprising asecond temperature sensing means, placed in said regenerator vesselbelow the point of introduction of said portion of thermal energy bysaid steam heat exchanger into said regenerator vessel, to control saidsteam heat exchanger.
 26. An apparatus according to claim 24 whereinsaid air heat exchanger has the surface area of at least 1200 squarefeet.
 27. An apparatus according to claim 25 wherein said steam heatexchanger has the surface area of at least 200 square feet.
 28. Anapparatus according to claim 26 wherein said air heat exchanger isplaced about the riser at a distance beginning at 15% to 70% of thetotal riser length and terminating at a distance of 20% to 90% of thetotal riser length.
 29. An apparatus according to claim 27 wherein saidsteam heat exchanger is placed about the riser at a distance beginningat 15% to 70% of the total riser length and terminating at a distance of20% to 90% of the total riser length.
 30. A process according to claim14 wherein the air heat exchanger is placed about the riser at adistance beginning at 20% to 50% of the total riser length andterminating at a distance of 25% to 90% of the total riser length.
 31. Aprocess according to claim 15 wherein the steam heat exchanger is placedabout the riser at a distance beginning at 20% to 50% of the total riserlength and terminating at a distance of 25% to 90% of the total riserlength.
 32. An apparatus according to claim 28 wherein said air heatexchanger is placed about the riser at a distance beginning at 20% to50% of the total riser length and terminating at a distance of 25% to90% of the total riser length.
 33. An apparatus according to claim 29wherein said steam heat exchanger is placed about the riser at adistance beginning at 20% to 50% of the total riser length andterminating at a distance of 25% to 90% of the total riser length.
 34. Aprocess according to claim 1, 15, 16, 17, 18, 30 or 31 wherein thetemperature in the upstream section of the riser is increased by atleast 2° F. over that obtainable without the heat exchanging means. 35.A process according to claim 34 wherein the temperature in the upstreamsection of the riser is increased by 5° F. to 50° F.
 36. A processaccording to claim 35 wherein the temperature in the upstream section ofthe riser is increased by 10° F. to 30° F.
 37. In a fluid catalyticcracking apparatus comprising a reactor vessel and a regenerator vessel,said reactor vessel comprising a riser divided into an upstream sectionand a downstream section, said regenerator vessel comprising aregenerating medium inlet conduit cooperating with a regenerating mediumdistribution means in the lower section thereof and a solid-gasseparation means in the upper section thereof, a means for conveying adeactivated catalyst from said reactor vessel to said regeneratorvessel, a means for conveying a regenerated catalyst from saidregenerator vessel to said reactor vessel, a first means for sensingtemperature at the outlet of said reactor vessel, said first means forsensing temperature controlling said means for conveying the regeneratedcatalyst from said regenerator vessel to said reactor vessel;theimprovement comprising equipping said riser with an air heat exchangerfor transferring at least a portion of thermal energy from said riser tosaid regenerator vessel, said portion of thermal energy being introducedinto said regenerator vessel above the regenerating medium distributionmeans; a second temperature sensing means, placed in said regeneratorvessel below the point of introduction of said portion of thermal energyby said air heat exchanger into said regenerator vessel to control saidair heat exchanger; said air heat exchanger being placed about the riserat a distance beginning at 15% to 70% of the total riser length andterminating at a distance of 20% to 90% of the total riser length; saidair heat exchanger having a surface area of at least 1200 square feet.38. In a fluid catalytic cracking apparatus comprising a reactor vesseland a regenerator vessel, said reactor vessel comprising a riser dividedinto an upstream section and a downstream section, said regeneratorvessel comprising a regenerating medium inlet conduit cooperating with aregenerating medium distribution means in the lower section thereof anda solid-gas separation means in the upper section thereof, a means forconveying a deactivated catalyst from said reactor vessel to saidregenerator vessel, a means for conveying a regenerated catalyst fromsaid regenerator vessel to said reactor vessel, a first means forsensing temperature at the outlet of said reactor vessel, said firstmeans for sensing temperature controlling said means for conveying theregenerated catalyst from said regenerator vessel to said reactorvessel;the improvement comprising equipping said riser with a steam heatexchanger for transferring at least a portion of thermal energy fromsaid riser to said regenerator vessel, said portion of thermal energybeing introduced into said regenerator vessel above the regeneratingmedium distribution means; a second temperature sensing means, placed insaid regenerator vessel below the point of introduction of said portionof thermal energy by said steam heat exchanger into said regeneratorvessel to control said steam heat exchanger; said steam heat exchangerbeing placed about the riser at a distance beginning at 15% to 70% ofthe total riser length and terminating at a distance of 20% to 90% ofthe total riser length; said steam heat exchanger having a surface areaof at least 200 square feet.
 39. A process according to claim 34 whereinthe reactor riser is positioned substantially vertically, and thehydrocarbonaceous feed and the catalyst admixed therewith are passedthrough the reactor riser in an upward direction.
 40. An apparatusaccording to claim 19, 28 or 29 wherein said riser is positionedsubstantially vertically, said upstream section is placed in the lowersection of the riser, and said downstream section is placed in the uppersection of the riser, above said upstream section.